1. Field of the Invention
The present invention relates to a capacitance sensor.
2. Description of the Related Art
A piping fluid decision device decides a fluid state of the fluid in a piping for sending fluid. An example of the piping fluid decision device, as shown in FIG. 1, includes a piping 101 for sending fluid, electrodes 103 and 105 inserted in the piping 101. The device is arranged at, for example, a beer factory or food shop, and decides a fluid state of beer as fluid. The device detects a conductivity in the piping 101 using the electrodes 103 and 105, and detects a difference of conductivity between a liquid part 109 and a froth part 111 of the beer 107; as a result, the device decides the fluid state of the beer 107 flowing in the piping 101. Depending on a result of the deciding, the froth part 111 of the beer 107 flowing in the piping 101 is wasted, as necessary, to surely take out the liquid part 109 of the beer 107.
According to the device, it is possible to take out the beer 107 with little froth anytime from a take-out machine installed at a terminal of the piping 101.
The device mentioned above, however, has some problems. The electrodes 103 and 105 are inserted in the piping, so that beer 107 flowing in the piping 101 directly contacts the electrodes 103 and 105. This corrodes the electrodes 103 and 105 to causes a sanitary problem. The device detects a variation of conductivity between the liquid part 109 and the froth part 111, so that voltage variations to be small are necessarily integrated, with an increased calculation amount. The detection of conductivity tends to be influenced by an associated magnetic field, as the result it is impossible to dispose the device in a vicinity of an electromagnetic valve.
If the fluid substance such as water flowing in the piping 101 includes a plurality of solid bodies such as metal, soil, or stone and is formed a solid fluid substance such as a metallic flow, soil flow, or stone flow, the fluid substance may collide on the electrodes 103 and 105 electrodes are kept from collision with the fluid substance. This causes the electrodes 103 and 105 to be damaged, and a failure of detection. Therefore, it is difficult, for the device having electrodes 103 and 105 inserted in a piping 101 shown as FIG. 1, to make a decision on a fluid state of the fluid substance including a plurality of solid bodies.